Cerebellar brain inhibition

The participants were seated in a chair, and their heads, trunks, and forearms were fixed. Motor cortex TMS was delivered using a figure-of-eight coil connected to a magnetic stimulator (The Magstim Co. Ltd, Whitland, UK). The maximum magnetic flux density of this coil was 1.2 T. Cerebellar TMS was delivered using a double-cone coil (YM-133B; Nihon Kohden, Tokyo, Japan) connected to a magnetic stimulator (SMN-1200; Nihon Kohden). The maximum magnetic flux density of this double-cone coil was 0.96 T. The figure-of-eight coil was then positioned at the hotspot for MEPs on the right first dorsal interosseous (FDI) muscle and the current in the coil was directed in the anterior to posterior direction. The center of the junction of the double-cone coil was placed 1 cm below and 3 cm to the right of the inion to stimulate the right cerebellum 4,18 and the current in the coil was directed downward. This induced an upwardly traveling current in the brain.

To record EMG signals, two surface-recording electrodes were placed 2 cm apart on the right FDI. The signals were amplified through an EMG amplifier (house-made) with a pass-band filter of 0.3 Hz–1 kHz and converted into digital signals at a sampling rate of 1 kHz using an analog-to-digital converter (USB-6008; National Instruments Co. Ltd, Austin, Texas, USA).

To calculate CBI, unconditioned and conditioned MEPs induced by cerebellar TMS were measured. In conditioning trials, cerebellar TMS was delivered before the test TMS over the contralateral M1. Interstimulus intervals (ISIs) of 1–8 ms were used 19. The intensity of the conditioning cerebellar TMS was set to 90% of the maximum output of the magnetic stimulator 18,20. To obtain a test MEP size of ∼1 mV 2, the intensity of the stimulator was adjusted before the examination and applied during the examination. Ten trials were conducted for each ISI. The intertest intervals were 5 s.